Method for producing flat glass, glass cullet to be used in the method

ABSTRACT

The present invention provides a method for manufacturing a glass sheet in which a raw material containing glass cullets is melted to form the glass sheet, wherein the glass cullets include a colored film and this colored film contains an alkali metal oxide, a silicon oxide, and fine particles containing carbon as their main component. The glass cullets can be recycled as a part of the raw material for glass in spite of the colored film included therein since in the glass cullets, the fine particles containing carbon as their main component are contained as a colorant.

TECHNICAL FIELD

The present invention relates to a method of manufacturing a glass sheetusing a glass sheet with a colored film as cullets.

BACKGROUND ART

In the field of glass for automobiles, as a glass sheet to be attachedto a car body with, for example, an adhesive, a glass sheet with acolored film is used in which its peripheral part is coated with aceramic color in order to prevent the adhesive from deteriorating due toultraviolet rays of sunlight and to provide it with a fine appearance.

The ceramic color contains about 20 mass % of pigment that includes ionsof transition metal such as, for instance, Cr, Fe, Co, Ni, or Cu as itsbase. In a conventional clear float glass, the amount of transitionmetal is less than 1%. Even a slight amount, for example, tens of ppm,of the transition metal affects its color tone and makes it perceivablethat the transition metal is contained therein. It therefore isimpossible at present to recycle the part coated with the ceramic colorby remelting it. This part may be used as a recycled material indirectlyfor other materials such as, for instance, roadbed materials or has tobe disposed as waste.

Conventionally, there were some glasses with a ceramic color containinglead. Recently, however, the use of lead has been limited for thepurpose of environmental protection.

New ceramic colors that are free from lead have been proposed andinclude, for instance, P₂O₅-based and alkali metaloxide-ZnO—B₂O₃—SiO₂-based ceramic colors.

The P₂O₅-based compositions are glass compositions and frit compositionsdisclosed in JP7(1995)-69672A, JP8(1996)-183632A, and JP9(1997)-208259A.

Furthermore, as the alkali metal oxide-ZnO—B₂O₃—SiO₂-based compositionis a ceramic color composition disclosed in JP8(1996)-133784A.

The respective compositions mentioned above, however, have problems suchas low acid resistance, a big difference in coefficient of expansion,etc. The aforementioned P₂O₅-based composition is composed of P₂O₅, analkali metal oxide, an alkaline earth oxide, etc. Hence, the temperaturedependency of its coefficient of expansion is higher than that of afloat glass having a soda-lime silica composition that often is used asa substrate. Such a difference in coefficient of expansion causes astrain in heating and cooling a glass substrate and degrades thestrength of a colored film and glass.

Moreover, the above-mentioned alkali metal oxide-ZnO—B₂O₃—SiO₂-basedcomposition contains 10% to 20% of B₂O₃ and 35% to 45% of ZnO andthereby has lower acid resistance.

Glasses coated with these ceramic colors are free from lead but containconsiderable amounts of P₂O₅, ZnO, B₂O₃, etc. that essentially are notcontained in a float glass as described above. Consequently, it isimpossible to use them as a cullet raw material to be used for a floatglass having a soda-lime silica composition.

DISCLOSURE OF THE INVENTION

With the above in mind, the present invention is intended to provide atechnique that allows a glass sheet with a colored film to be used as amaterial for a glass required to be of high quality, especially ascullets to be used in the float process.

As a result of keen studies made assiduously, in the present invention,a colored film that coats at least a part of a surface of a glasssubstrate is formed with fine particles containing carbon as their maincomponent dispersed in a film containing a silicon oxide and an alkalimetal oxide.

In the present specification, the “main component” denotes a componentthat accounts for at least 50 mass % of the whole.

This colored film can be formed as one having a light-shielding functionthrough the use of the fine particles containing carbon as their maincomponent even when it is substantially free from transition metal suchas Cr, Fe, Co, Ni, or Cu that serves as a colorant.

In this connection, the expression “substantially free” denotes that theamount of transition metal contained therein as an impurity is allowableand specifically, is in the range of not more than about 1 mass %,preferably in the range of not more than 100 ppm.

When the glass substrate with the colored film is used as cullets to bea part of a raw material for glass, the fine particles containing carbonas their main component that serves as a colorant react with oxygen whenmelting the raw material to become carbon dioxide and volatilize. Hence,the molten glass is not colored. Consequently, the glass substrate withthe colored film readily can be recycled as cullets.

In other words, according to one aspect of the present invention, thereare provided a method of manufacturing a glass sheet in which a rawmaterial including glass cullets is melted to form the glass sheet,wherein the glass cullets include a colored film and this colored filmcontains an alkali metal oxide, a silicon oxide, and fine particlescontaining carbon as their main component, and a glass sheet obtained bythis method.

According to another aspect of the present invention, there are providedglass cullets that include both glass cullets including a colored filmand those including no colored film, wherein the colored film containsan alkali metal oxide, a silicon oxide, and fine particles that includecarbon as their main component.

The glass cullets can be used as a part of the raw material for glasswithout requiring a bothersome process of removing the cullets includinga colored film formed thereon to obtain the cullets including no coloredfilm.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional partial view showing an example of a glasssheet with a colored film that provides cullets of the presentinvention.

FIG. 2 is a cross-sectional view showing an example of a glass sheetwith a colored film that provides cullets of the present invention.

FIG. 3 is a cross-sectional view showing an example of a laminated glassincluding a glass sheet with a colored film that provides cullets of thepresent invention.

FIG. 4 is a plan view showing an example of a laminated glass includinga glass sheet with a colored film that provides cullets of the presentinvention.

FIG. 5 is a diagram showing the configuration of a float apparatus thatcan be used for carrying out the method of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Generally, a float glass contains, as its main components, an alkalimetal oxide, an alkaline earth metal oxide, and SiO₂. In order to use aglass sheet with a colored film as a cullet raw material for a floatglass, it is preferable that the colored film is substantially free fromcomponents that generally are not contained in a float glass, forexample, TiO₂, ZnO, ZrO₂, P₂O₅, or La₂ ₃. Furthermore, it is preferablethat the colored film is substantially free from transition metal thatcan be a coloring component, for example, Ti, V, Cr, Mn, Fe, Co, Ni, Cu,or Mo.

Particularly, when a glass sheet with a colored film containing CoO,Cr₂O₃, CuO, NiO, or MnO is mixed in as a cutlet raw material for a clearglass or glass containing a different coloring component from that ofthe colored film, it is difficult to obtain a glass sheet having desiredoptical characteristics (transparency, coloration, etc.). Preferably,the colored film is substantially free from these metal oxides. Inaddition, cadmium sulfide or antimony sulfide may form colloids in glassto color the glass in some cases. Accordingly, it is preferable that thecolored film is substantially free from these elements and compoundsthereof. With consideration given to the environment, it is preferablethat the colored film is substantially free from lead.

From the viewpoints mentioned above, it is preferable that the coloredfilm is substantially free from Ti, Zn, Zr, P, La, Co, Cr, Cu, Ni, Mn,Cd, Sb, and Pb.

The fine particles containing carbon as their main component serve as acolorant that does not prevent the glass sheet from being recycled ascullets. In order to use the fine particles, it is preferable that thecolored film is formed to be an amorphous film (a vitreous film) andthereby the oxygen-shielding function of the colored film is secured.This can prevent the fine particles containing carbon as their maincomponent from being oxidized even if the glass substrate is heated to ahigh temperature in forming the colored film. In order to allow thecolored film to be vitreous, it may contain an alkali metal oxide and asilicon oxide.

Preferably, the colored film contains, in terms of mass %:

-   8% to 23% of alkali metal oxide;-   40% to 75% of silicon oxide; and-   3% to 45% of fine particles,    and more preferably,-   10% to 23% of alkali metal oxide;-   49% to 73% of silicon oxide; and-   16% to 40% of fine particles.

When the film is formed of silicon oxide alone, the fine particlescontaining carbon as their main component may be burnt in a hightemperature atmosphere employed, for example, in a step of sintering thecolored film. The alkali metal oxide inhibits the burning.

The colored film may contain one type of alkali metal oxide butpreferably, it contains at least two types of alkali metal oxides. Theuse of at least two types of alkali metal oxides makes it possible toobtain a hard colored film that is excellent in moisture resistance andchemical resistance (acid resistance and alkali resistance).

The phenomenon that generally is referred to as a “mixed alkali effect”is one that when a part of alkali is substituted by another alkalielement, its characteristics deviate from the sum rule considerably evenwhen the total content of alkali is not changed. Examples ofcharacteristics that are changed considerably by the mixed alkali effectinclude chemical resistance that is typified by water resistance, acidresistance, and alkali resistance, electrical conductivity, and adiffusion coefficient.

The mixed alkali effect in an amorphous and vitreous colored film lowersthe mobility of alkali, suppresses alkaline elution, and thereby canimprove the moisture resistance.

The following description is directed to a preferred embodiment of thecolored film and reasons for limiting its components. The contents ofcomponents described bellow are indicated in mass %.

When the alkali metal oxide includes only one type of alkali metal, itis advantageous that this alkali metal is sodium.

With respect to Na₂O, it is not preferable that its content is less than1%, because less than 1% of Na₂O results in deterioration in alkaliresistance of the colored film and an excessively low coefficient ofthermal expansion that in turn degrades the strength of the glass andcolored film. A preferred content of Na₂O is at least 5%. On the otherhand, it also is not preferable that the content of Na₂O exceeds 18%,because more than 18% of Na₂O results in an excessively high coefficientof thermal expansion that causes a large shrinkage of the film when itis dried or sintered and thereby cracks tend to occur in the coloredfilm. A further preferred content of Na₂O is 15% or less.

When at least two types of alkali metal oxides are included, it isadvantageous that the at least two types of alkali metal oxides include,together with sodium, at least one selected from potassium and lithium.

K₂O and/or Li₂O improves the moisture resistance and chemical resistanceof the colored film when being contained together with Na₂O. When thetotal content of K₂O and Li₂O is less than 0.1%, the water resistanceand the moisture resistance cannot be improved satisfactorily.Accordingly, the total content is preferably at least 1%. The totalcontent of K₂O and Li₂O exceeding 19% results in an excessively highcoefficient of thermal expansion that causes a large shrinkage of thefilm when it is dried or sintered, as in the case of Na₂O. This resultsin cracks tending to occur in the colored film. The total content of K₂Oand Li₂O is preferably 12% or less.

The content of K₂O is preferably 18% or less, more preferably 11% orless, while the content of Li₂O is preferably 10% or less, morepreferably 5% or less.

The silicon oxide is, for example, SiO₂, and SiO₂ serves as a networkformer in a vitreous film. A content of SiO₂ of less than 40% results indegradation in the strength of the colored film and also causes thealkali resistance to deteriorate. Hence, the content of SiO₂ ispreferably at least 40%, more preferably at least 50%.

On the other hand, a content of SiO₂ exceeding 70% results in a lowercoefficient of thermal expansion. This results in a greater differencein coefficient of thermal expansion with that of a glass having asoda-lime silica composition. Furthermore, unlike the glass, the coloredfilm is subjected to not only the shrinkage caused by the thermalexpansion but also that caused by moisture loss. The shrinkage caused bythe moisture loss is suppressed by the presence of alkali and theshrinkage caused by the thermal expansion therefore dominates. Hence, itis preferable that the content of SiO₂ is 70% or less.

The fine particles containing carbon as their main component affect thefilm strength as well as alkali resistance depending on their ratio tothe silicon oxide and alkali metal oxide. Hence, it is preferable thatthe content of the colorant to be added is specifically in the range of15% to 40%, more preferably in the range of 15% to 35%.

With consideration given to the above, it is preferable that the coloredfilm contains, in terms of mass %:

-   1% to 18% of Na₂O;-   0% to 18% of K₂O ;-   0% to 10% of Li₂O;-   0.1% to 19% of K₂O +Li₂O;-   40% to 70% of SiO₂; and-   15% to 40% of fine particles,    and more preferably,-   5% to 15% of Na₂O;-   0% to 11% of K₂O;-   0% to 5% of Li₂O;-   1% to 12% of K₂O+Li₂O;-   50% to 70% of SiO₂; and-   15% to 35% of fine particles.

Examples of the fine particles containing carbon as their main componentinclude carbon black, black lead (graphite) composed of carbon alone,azo pigment, phthalocyanine pigment, and fused polycyclic pigment, and apreferable form thereof is the form of fine particles. Carbon black fineparticles are further preferable. Various carbon blacks are manufacturedthat have different characteristics depending on the manufacturingmethods to be employed. Any of the carbon blacks may be used. Examplesof carbon blacks manufactured by different methods include acetyleneblack, channel black, furnace black, and Ketjenblack (the trade name ofa product of Lion Corporation). The diameter of the fine particles isnot particularly limited.

The carbon black reacts with oxygen to become carbon dioxide andvolatilizes not only at 1000° C. or higher but also at a temperatureclose thereto. Usually, a float glass is manufactured by heating a rawmaterial to at least 1000° C. to melt it and then forming it into afloat glass. Hence, in this melting process, the carbon blackvolatilizes and thus does not affect the coloration of the glass.Accordingly, when consideration is given to the recyclability, carbonblack is a preferable colorant. Furthermore, since the carbon blackprovides a black appearance, it also is suitable as a ceramic color ofglasses for automobiles.

The colored film contains an alkali metal oxide and fine particles andtherefore shrinks less during its formation than a film formed of asilicon oxide alone. Accordingly, the stress caused between the coloredfilm and the substrate can be eased.

For example, when a thick vitreous film is to be formed directly by asol-gel process, cracks occur due to the stress caused between itselfand the substrate. Hence, in order to obtain a thick film, a pluralityof thin films that each cause less stress have to be formed to bestacked together.

On the contrary, application of the above makes it possible to obtain afilm having a desired thickness, for instance, a colored film with athickness of 1 to 20 μm, through film formation carried out only once.When a film is formed of a silicon oxide and fine particles alone, itmerely can have a thickness of about several hundreds of nanometers.

In the case where it is necessary to further improve the waterresistance and moisture resistance of the colored film, the colored filmmay be subjected to dealkalization after its formation. The alkali metaloxide is a component that is essential in forming the colored film to beamorphous to secure its oxygen-shielding function. Hence, for example, acolored film is allowed to contain plenty of alkali metal oxide(preferably at least 8 mass %) when being sintered in the heating stepand thereby is formed as an amorphous film that is excellent in theoxygen-shielding function, and thereafter, the alkali metal oxide isreduced (preferably to 5 mass % or less). This eases the oxidation ofthe fine particles containing carbon as their main component andprevents the colored film from deteriorating.

A polar solvent is not particularly limited. However, it is advantageousthat the polar solvent contains, for example, at least one selected fromwater and alcohol with a carbon number of 3 or smaller, preferablywater. The polar solvent may contain acid. Particularly, an aqueoussolution containing acid is suitable for the reduction of the alkalimetal oxide. The water is not particularly limited and may be, forinstance, tap water, distilled water, or ion exchanged water.

The acid is not particularly limited. As the acid may be used variousacids defined in, for instance, Arrhenius, Bronsted-Lowry, Lewis, Cady &Elsey. The acid may be organic acid but at least one inorganic acidselected from hydrochloric acid, sulfuric acid, nitric acid,hydrofluoric acid, and phosphoric acid is suitable.

When acid is used, it is preferable that a step of reducing the acidcontained in the colored film, i.e. a neutralization step, is carriedout by bringing at least a polar solvent into contact with the coloredfilm additionally after a polar solvent containing acid is brought intocontact therewith.

As the solvent to be used for the neutralization may be employed, forinstance, water as in the above or a basic solution containing ahydroxyl group-containing compound such as, for example, NaOH, Ca(OH)₂,or Al(OH)₃.

The method of bringing a solvent into contact with the colored film isnot particularly limited but may be immersion into a solvent (solution)or application with, for instance, cloth containing a solvent(solution).

It is preferable that after the dealkalization, the colored filmcontains 5 mass % of alkali metal oxide or less, and furtherspecifically, in terms of mass %:

-   0.1% to 5% of alkali metal oxide;-   55% to 90% of silicon oxide; and-   10% to 45% of fine particles.

It is preferable that the content of alkali metal oxide is as small aspossible but the alkali metal oxide has no substantial influence as longas its content is 5 mass % or less.

In the glass sheet with the colored film that provides glass cullets ofthe present invention, as shown in FIG. 1, a colored film 2 is formed ona glass sheet 1. As shown in FIG. 2, a glass sheet 1 may be bent. Inthis glass sheet 1, a colored film 2 is formed on its peripheral part.As shown in FIG. 3, a laminated glass may be formed in which a glasssheet 1 (a first glass sheet) with a colored film 2 formed thereon andanother glass sheet (a second glass sheet) 3 are joined together with athermoplastic resin film 4 such as polyvinyl butyral (PVB). As shown inFIG. 4, this laminated glass can be used as a windshield with thecolored film 2 arranged in the form of a frame.

The glass sheets shown in the drawings also are examples of glass sheetsthat can be provided by the manufacturing method of the presentinvention. Glass sheets formed from a raw material containing glasscullets can be used as window glasses for buildings, window glasses forvehicles, etc. after they are subjected to, for example, at least oneprocess selected from a tempering process and a bending process asrequired and in some cases, further a laminating process and theformation of a colored film.

Scrapped glass sheets are crushed to become glass cutlets. From therespective glass sheets shown in the drawings are obtained glass culletsincluding cullets both with and without a colored film. The presentinvention makes it possible to avoid the selection of the glass culletsand the disposal of the glass cullets as industrial waste due to thetroublesomeness of the selection.

The float process using the glass cullets as a part of a raw materialfor glass can be carried out according to the conventional method. Forinstance, as shown in FIG. 5, the raw material for glass is put into amelting furnace 10 to be melted at, for example, 1300° C. to 1500° C.and thereby a glass sheet is formed to have a predetermined thickness onmolten tin inside a float furnace 11, which then is cooled in anannealing furnace 12. The glass cullets mixed into the raw material forglass allow the raw material for glass to be melted readily and reducethe energy required for the melting.

In the raw material for glass there may be used, together with the glasscullets, raw materials used commonly, for example, silica sand,Glauber's salt, limestone, and dolomite. With consideration given to thefunction, as a reductant, of carbon provided by the colored film, it ispreferable that a required amount of oxidizer is added thereto. When thecarbon functions as a reductant, iron contained in the glass is reducedexcessively and thereby the content of Fe²⁺ may increase to cause colordevelopment that is undesirable for the glass.

A preferable oxidizer is at least one selected from nitrate and sulfateof sodium, sodium sulfate, and/or sodium nitrate. This oxidizer oxidizesorganic compounds contained in a prepared batch of the raw material forglass to inhibit iron from being reduced. Furthermore, the sodiumsulfate helps bubbles remaining in molten glass to be clarified and aglass melt to be homogenized.

The amount of oxidizer to be added depends on the amount of carbonformed in cullets that become a glass melt, the redox equilibrium stateof the glass melt, etc. It, however, is advantageous that at least anamount of oxidizer is added that is larger than that of the reductantpresent in the glass melt containing cullets.

The manufacturing method in which the above-mentioned amount of oxidizeris added to the raw material is suitable for the manufacture of glasssheets containing iron whose total content expressed in terms of Fe₂O₃is at least 0.05 mass %, further at least 0.3 mass %, and particularlyat least 0.5 mass %. The iron includes bivalent iron and trivalent ironthe ratio between which varies depending on its redox state and thusconsiderably affects the color tone of the glass.

EXAMPLES Example 1

About 400 g of glass cullets including a colored film whose amount wasabout 0.1% in terms of mass % that had been formed on a glass sheet wasmelted in a platinum crucible at 1500° C. for two hours. Glass thusobtained was maintained at 650° C. for 45 minutes and then was cooled toroom temperature. Thus, a sample was obtained.

This sample was ground to have a thickness of 5 mm and then its opticalcharacteristics were measured (see Table 1). In Table 1, YA denotesvisible light transmittance (%), TG solar radiation transmittance (%),Tuv ultraviolet transmittance (%), λd a dominant wavelength (nm), and Peexcitation purity. In addition, x and y indicate chromaticitycoordinates obtained in the method of indicating chromaticity by thedominant wavelength and excitation purity. Furthermore, L*, a*, and b*denote psychometric lightness and psychometric chroma coordinatesaccording to the L*a*b* color system. The colored film was formed by thefollowing method.

First, 30 g of sodium silicate solution, 20 g of colloidal silica, and50 g of carbon black (LION PASTE W-311N, manufactured by LionCorporation) were weighed and then were mixed together. Thus, a solutioncontaining fine particles to be used for forming a colored film (aliquid composition) was obtained that included a solid content of 3% ofNa₂O, 13% of SiO₂, and 8% of carbon.

In this connection, the concept of the “solid content” is used in thefield of, for example, the sol-gel process and the “solid content”denotes components contained in a solid body such as a film formed froma liquid composition. The “solid content” also includes components thathave been dissolved in the liquid composition besides the fineparticles.

This liquid composition was applied, with a spin coater, to the surfaceof a washed glass substrate having a soda-lime silicate glasscomposition. This was dried at room temperature for five minutes andthen in a drying furnace at 190° C. for 30 minutes. Thereafter, thisglass substrate was put into a sintering furnace whose temperature hadbeen raised to 680° C. and thereby the colored film applied thereto wassintered for 120 seconds. The colored film thus obtained had a thicknessof about 5 μm.

Example 2

About 200 g of glass cullets including a colored film whose amount wasabout 0.1% in terms of mass % that had been formed on a glass sheet anda material composed of a batch of 200 g having the same composition andthe same FeO ratio as those of the glass cullets and sodium sulfateadded thereto as an oxidizer were melted in a platinum crucible at 1500°C. for two hours.

Glass thus obtained was maintained at 650° C. for 45 minutes and thenwas cooled slowly to room temperature. Thus, a sample was obtained. Thissample was ground to have a thickness of 5 mm and then its opticalcharacteristics were measured (see Table 1). The colored film wasobtained in the same manner as in Example 1.

Reference Example 1

400 g of glass cullets including no colored film was melted in aplatinum crucible at 1500° C. for two hours. Glass thus obtained wasmaintained at 650° C. for 45 minutes and then was cooled to roomtemperature. Thus, a sample was obtained. This sample was ground to havea thickness of 5 mm and then its optical characteristics were measured(see Table 1). TABLE 1 Reference Example 1 Example 2 Example 1 GlassThickness (mm) 4.99 4.99 4.99 YA (%) 75.6 77.0 76.9 TG (%) 47.3 50.050.0 Tuv 26.5 25.7 25.8 λd (nm) 493.3 495.4 495.4 Pe 4.56 3.60 3.60 x0.2973 0.2997 0.2997 y 0.3187 0.3200 0.3200 L* 90.52 91.00 90.99 a*−7.58 −7.02 −7.02 b* −1.17 −0.33 −0.33

With respect to the optical characteristics of Example 1, the variationsin all the visible light transmittance, the solar radiationtransmittance, and the ultraviolet transmittance from those of thereference example were within 3%. Furthermore, the visible lighttransmittance (75.6%) of Example 1 was higher than the standard valuerequired for glasses for automobiles.

Moreover, no amber color developed by carbon was observed. All thevariations in values concerning the color tone such as those of theexcitation purity, the dominant wavelength, psychometric lightness, etc.also were within 1%.

The carbon amber is a phenomenon that Fe or Na reacts with SO₄ ²⁻ thatis a S component contained in the glass, in a reducing atmosphere (inthe presence of carbon) and the coloration of colloid generated therebyexhibits a blackish brown (i.e. an amber).

All the optical characteristics of Example 2 were substantially the sameas those of Reference Example. As a result, it was confirmed that evenwhen glass cullets including a colored film containing carbon as acolorant were used as a part of the raw material, the use of an oxidizertogether with the glass cullets prevented any effects on coloring of aglass from being caused in manufacturing the glass. The sample ofExample 2 contained about 0.5% of iron in terms of Fe₂O₃.

Example 3

30 g of sodium silicate solution (Water Glass No.3, manufactured byKISHIDA CHEMICAL CO., LTD., hereinafter also referred to as “waterglass”), 20 g of colloidal silica (PC500, manufactured by NISSANCHEMICAL INDUSTRIES, LTD.), and 50 g of carbon black (LION PASTE W-311N,manufactured by Lion Corporation) were weighed and then were mixedtogether. Thus, a liquid composition for forming a colored film wasobtained that included a solid content of 3% of Na₂O, 13% of SiO₂, and8% of carbon. Table 2 shows the ratios of the solid content included inthe liquid composition.

This liquid composition was applied, with a bar coater, to the surfaceof a washed glass substrate (100×100×2.1 mm) having a soda-lime silicateglass composition. This was dried at room temperature for five minutesand then in a drying furnace at 190° C. for 40 minutes. Thereafter, thisglass substrate was put into a sintering furnace whose temperature hadbeen raised to 720° C. and thereby the colored film applied thereto wassintered for 90 seconds. The colored film thus obtained had a thicknessof about 5 μm. Table 2 shows the composition of the colored film and theconditions under which the colored film was formed.

The visible light transmittance and ultraviolet transmittance of theglass sheet with the colored film thus obtained were measured with aspectrophotometer (UVPC-3100, manufactured by Shimadzu Corporation). Asa result, the visible light transmittance and ultraviolet transmittanceeach were 0.1% or lower with respect to the entire wavelength regionconcerned. Thus, it was proved that the colored film had alight-shielding function (see Table 2).

In order to examine the acid resistance and alkali (base) resistance ofthe colored film, the following test was carried out. That is, with aspectro-photometric type calorimeter (SE-2000, manufactured by NipponDenshoku Industries Co., Ltd.) variations in lightness of the glasssurface and the film surface caused when the glass sheet with thecolored film was immersed in 0.1N sulfuric acid (an acid resistancetest) and 0.1N sodium hydroxide (an alkali resistance test) solutionsfor 24 hours were determined.

As a result of the acid resistance test and alkali resistance test, itwas proved that the lightness of both the colored film surface and theexposed glass surface did not vary. That is, it was proved that thecolored film according to the present invention had an excellentresistance to acid and alkali.

The evaluation of hardness of the colored film was carried out using aTaber abrasion tester (5150 ABRASER, TABER INDUSTRIES) by rotating anabrasion ring against the glass sheet with the colored film 1000 timesat a load of 500 g and determining the variations in transmittancecaused between before and after the test. As a result, in the coloredfilm according to the present invention, the transmittances obtainedbefore and after the test did not vary with each other. Thus, it wasproved that the colored film had considerably high hardness andexcellent abrasion resistance (see Table 2).

Furthermore, in order to examine, in a simple manner, the influence thatis caused when the liquid composition for forming the colored film isremelted as a cullet raw material in manufacturing glass, ahigh-temperature melting test was carried out. In the test, the liquidcomposition was heated up to 1300° C. at a heating rate of 10° C./minusing a TG-DTA analyzer (thermal analysis equipment TAS-100,manufactured by Rigaku Corporation).

The liquid composition thus melted was observed visually. Consequently,it was confirmed that the carbon serving as a colorant had been burnt todisappear and thereby the liquid composition was transparent. As aresult, it was proved that the colored film had no influence on thecoloration of the glass sheet even if it was contained in the cutlet rawmaterial used in manufacturing the glass sheet. TABLE 2 Examples 3 4 5 67 8 9 Ratios of Solid Content included in Liquid Composition Na₂O (%) 1212 19 11 12 12 12 SiO₂ (%) 53 52 65 50 53 53 53 C (%) 35 36 16 39 35 3535 Conditions under which films were formed Pre-drying Room Room RoomRoom Room Room Room Temperature Temperature Temperature TemperatureTemperature Temperature Temperature Temperature (° C.) Pre-drying 5 5 560 120 20 20 Time (min) Post-drying 190 190 190 190 — 140 240Temperature (° C.) Post-drying 40 15 30 15 — 60 20 Time (min) Sintering720 620 680 720 720 620 720 Temperature (° C.) Sintering 90 600 120 9080 240 80 Time (sec) Film Composition Na₂O (%) 16 19 12 21 14 17 15 SiO₂(%) 61 73 75 59 58 74 66 C (%) 23 8 13 20 28 9 19 Film CharacteristicsUltraviolet <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 and Visible-LightTransmittance (%) Acid and Good Good Good Good Good Good Good BaseResistance Abrasion Good Good Good Good Good Good Good Resistance High-Good Good Good Good Good Good Good Temperature Melting Test*1 With respect to the acid and base resistance, “Good” indicates avariation in lightness ΔL of 1 or less.*2 With respect to the abrasion resistance, “Good” indicates a variationin visible light transmittance of 1% or less.*3 In the high-temperature melting test, “Good” indicates no coloringobserved visually.

Example 4

30 g of sodium silicate solution, 20 g of colloidal silica, and 50 g ofcarbon black (LION PASTE W-310A, manufactured by Lion Corporation) wereweighed and then were mixed together. Thus, a liquid composition wasobtained that included a solid content of 3% of Na₂O, 13% of SiO₂, and9% of carbon.

This liquid composition was applied, with a spin coater, to the surfaceof a washed glass substrate having a soda-lime silicate glasscomposition. This was dried at room temperature for five minutes andthen in a drying furnace at 190° C. for 30 minutes. Thereafter, thisglass substrate was put into a sintering furnace whose temperature hadbeen raised to 680° C. and thereby the colored film applied thereto wassintered for 120 seconds. The colored film thus obtained had a thicknessof about 5 μm (see Table 2).

The visible light transmittance and ultraviolet transmittance of theglass sheet with the colored film thus obtained each were 0.1% or lowerwith respect to the entire wavelength region concerned. Thus, it wasproved that the glass sheet with the colored film had a light-shieldingfunction. Furthermore, various tests were carried out in the same manneras in Example 3. Table 2 shows the results.

Examples 5 to 9

Glass sheets each provided with one of colored films having various filmcompositions indicated in Table 2 were produced and theircharacteristics were evaluated in the same manner as in Example 3. Theresults also are shown in Table 2.

As the results of Examples 5 to 9, the visible light transmittance andultraviolet transmittance of all the glass sheets each provided with oneof the colored films each were 0.1% or lower with respect to the entirewavelength region concerned. Thus, it was proved that they had alight-shielding function.

Moreover, as a result of melting the liquid compositions for forming thecolored films at a high temperature, it was confirmed that in the liquidcompositions thus melted, carbon had been burnt to disappear and therebythe liquid compositions were transparent.

Example 10

30 g of sodium silicate solution (Water Glass No.3, manufactured byKISHIDA CHEMICAL CO., LTD.), 20 g of colloidal silica (PC500,manufactured by NISSAN CHEMICAL INDUSTRIES, LTD.), and 50 g of carbonblack (LION PASTE W-311N, manufactured by Lion Corporation) were weighedand then were mixed together. Thus, a liquid composition for forming acolored film was obtained that included a solid content of 3% of Na₂O,13% of SiO₂, and 8% of carbon.

This liquid composition was applied, with a bar coater, to the surfaceof a washed glass substrate (150×150×2.1 mm) having a soda-lime silicateglass composition. This was dried at room temperature for five minutesand then in a drying furnace at 190° C. for 10 minutes. Thereafter, thisglass substrate was put into a sintering furnace whose temperature hadbeen raised to 720° C. and thereby the colored film applied thereto wassintered for 120 seconds. Furthermore, the glass coated with the coloredfilm was immersed in 0.1N sulfuric acid for two hours to be subjected todealkalization. Subsequently, acid remaining on the surface was washedoff with water and superfluous water was wiped off with cloth. Thecolored film thus obtained had a thickness of about 10 μm. Table 3 showsthe composition of the film that has been subjected to thedealkalization.

The visible light transmittance and ultraviolet transmittance of theglass sheet with the colored film thus obtained each were 0.1% or lowerwith respect to the entire wavelength region concerned. Thus, it wasproved that glass sheet had a light-shielding function of the coloredfilm (see Table 3).

From the results of the acid resistance test and the alkali resistancetest, it was proved that the lightness of both the colored film surfaceand the exposed glass surface did not vary.

In addition, the evaluation of hardness of the film was carried out inthe same manner as in Example 3. As a result, transmittances obtainedbefore and after the test did not vary with each other. Thus, it wasproved that the colored film had considerably high hardness.

Furthermore, the liquid composition for forming the colored film wasmelted at a high temperature and thereby the meltability of the colorantwas tested. As a result, it was confirmed that in the liquid compositionobtained thus melted, carbon had been burnt to disappear and thereby theliquid composition was transparent.

Moreover, in order to check the moisture resistance, variations inlightness of the glass surface and the film surface caused after theglass sheet with the colored film was maintained, for 400 hours, insidea temperature and humidity tester (JLH-300, manufactured by ETACEngineering Co.) that was kept at 50° C. and a RH of 95% were determinedwith a spectro-photometric type calorimeter (SE-2000, manufactured byNippon Denshoku Industries Co., Ltd.), and the film condition wasobserved visually. As a result, no variations in lightness were found inboth the glass surface and the film surface, and peeling of the coloredfilm did not occur.

Examples 10 to 12

Glass sheets each provided with one of colored films having various filmcompositions indicated in Table 3 were produced and theircharacteristics were evaluated in the same manner as in Example 7. Theresults also are shown in Table 3.

As the results of Examples 10 to 12, the visible light transmittance andultraviolet transmittance of all the glass sheets each provided with oneof the colored films each were 0.1% or lower with respect to the entirewavelength region concerned. Thus, it was proved that they had alight-shielding function.

Moreover, as a result of melting the liquid compositions for forming thecolored films at a high temperature, it was confirmed that in the liquidcompositions thus melted, carbon had been burnt to disappear and therebythe liquid compositions were transparent. TABLE 3-1 Example 10 Example11 Example 12 Film Composition Before Dealkalization Na₂O (%) 12 19 11SiO₂ (%) 53 65 50 C (%) 35 16 39 Film Composition After DealkalizationNa₂O (%) 1 1 0.4 SiO₂ (%) 59 78 83.6 C (%) 40 21 16 Conditions underwhich films were formed Pre-drying Room Room Room Temperature (° C.)Temperature Temperature Temperature Pre-drying Time 5 5 15 (min)Post-drying 190 190 190 Temperature (° C.) Post-drying Time 10 30 15(min) Sintering 720 720 720 Temperature (° C.) Sintering Time 120 90 90(sec) Dealkalization 2 2 24 Time (hr)

TABLE 3-2 Example Example Example Film Characteristics 10 11 12Ultraviolet and <0.1 <0.1 <0.1 Visible-Light Transmittance (%) Acid andBase Good Good Good Resistance Abrasion Good Good Good ResistanceHigh-Temperature Good Good Good Melting Test Moisture Good Good GoodResistance

1. A method for manufacturing a glass sheet comprising melting a raw material, and forming the melted raw material to a glass sheet, wherein the raw material comprises glass cullets, and wherein the glass cullets comprise a colored film, and the colored film comprises an alkali metal oxide, a silicon oxide, and fine particles that include carbon as their main component.
 2. The method for manufacturing a glass sheet according to claim 1, wherein the raw material comprises an oxidizer.
 3. The method for manufacturing a glass sheet according to claim 2, wherein the oxidizer comprises at least one selected from the group consisting of sulfate and nitrate of sodium.
 4. The method for manufacturing a glass sheet according to claim 1, wherein the fine particles that include carbon as their main component are carbon black fine particles.
 5. The method for manufacturing a glass sheet according to claim 1, wherein the colored film is substantially free from transition metal.
 6. The method for manufacturing a glass sheet according to claim 1, wherein the colored film is substantially free from Ti, Zn, Zr, P, La, Co, Cr, Cu, Ni, Mn, Cd, Sb, and Pb.
 7. A glass sheet obtained by the manufacturing method according to claim
 1. 8. The glass sheet according to claim 7, wherein the glass sheet comprises iron and a total amount of the iron is 0.05 mass % or more in terms of Fe₂O₃.
 9. Glass cullets, comprising both a glass cullet that includes a colored film and a glass cullet that includes no colored film, wherein the colored film comprises an alkali metal oxide, a silicon oxide, and fine particles that include carbon as their main component. 